Osteoprotegerin ligand is a cytokine that regulates osteoclast differentiation and activation

Applications of Gene Therapy in Dentistry: A Review Article

Gene therapy promises to possess a good prospect in bridging the gap between dental applications and medicine. The dynamic therapeutic modalities of gene therapy have been advancing rapidly. Conventional approaches are being revamped to be more comprehensive and pre-emptive, which could do away with the need for surgery and medicine altogether. The complementary base sequences known as genes convey the instructions required to manufacture proteins. The oral cavity is one of the most accessible locations for the therapeutic intervention of gene therapy for several oral tissues. In 1990, the first significant trial of gene therapy was overseen to alleviate adenosine deaminase deficiency. The notion of genetic engineering has become increasingly appealing as a reflection of its benefits over conventional treatment modalities. An example of how this technology may alter dentistry is the implementation of gene therapy for dental and oral ailments. The objective of this article is to examine the effects of gene therapy on the field of dentistry, periodontology and implantology. Furthermore, the therapeutic factors of disease therapy, minimal invasion, and appropriate outcome have indeed been taken into consideration.

Bone circuitry and interorgan skeletal crosstalk

The past decade has seen significant advances in our understanding of skeletal homeostasis and the mechanisms that mediate the loss of bone integrity in disease. Recent breakthroughs have arisen mainly from identifying disease-causing mutations and modeling human bone disease in rodents, in essence, highlighting the integrative nature of skeletal physiology. It has become increasingly clear that bone cells, osteoblasts, osteoclasts, and osteocytes, communicate and regulate the fate of each other through RANK/RANKL/OPG, liver X receptors (LXRs), EphirinB2-EphB4 signaling, sphingolipids, and other membrane-associated proteins, such as semaphorins. Mounting evidence also showed that critical developmental pathways, namely, bone morphogenetic protein (BMP), NOTCH, and WNT, interact each other and play an important role in postnatal bone remodeling. The skeleton communicates not only with closely situated organs, such as bone marrow, muscle, and fat, but also with remote vital organs, such as the kidney, liver, and brain. The metabolic effect of bone-derived osteocalcin highlights a possible role of skeleton in energy homeostasis. Furthermore, studies using genetically modified rodent models disrupting the reciprocal relationship with tropic pituitary hormone and effector hormone have unraveled an independent role of pituitary hormone in skeletal remodeling beyond the role of regulating target endocrine glands. The cytokine-mediated skeletal actions and the evidence of local production of certain pituitary hormones by bone marrow-derived cells displays a unique endocrine-immune-skeletal connection. Here, we discuss recently elucidated mechanisms controlling the remodeling of bone, communication of bone cells with cells of other lineages, crosstalk between bone and vital organs, as well as opportunities for treating diseases of the skeleton.

Prolactin regulates RANKL expression via signal transducer and activator of transcription 5a signaling in mammary epithelial cells of dairy cows

Receptor of activated nuclear factor kappa B ligand (RANKL) is regulated by prolactin in the mammary gland. However, the intrinsic molecular mechanism is not well understood. Herein, mammary epithelial cells (MECs) of dairy cows were isolated to characterize the molecular mechanism of prolactin in vitro. We demonstrated that prolactin stimulation increased the expression of RANKL in MECs. Moreover, the expression of RANKL induced by prolactin was inhibited by the prolactin receptor or signal transducer and activator of transcription 5A (STAT5a) knockdown. Furthermore, prolactin markedly increased RANKL-Luciferase reporter activity in MECs. We identified a putative gamma-interferon activated site (GAS) in the region between residues -883 to -239 bp of the RANKL promoter. Subsequently, we found that the mutated GAS sequence failed to respond to prolactin stimulation. In addition, STAT5a knockdown markedly decreased prolactin-stimulated RANKL promoter activity. Western blot results revealed that RANKL overexpression markedly decreased the STAT5a phosphorylation level in MECs. These findings indicate that prolactin could regulate RANKL promoter activity via STAT5a, contributing to increased RANKL expression in MECs. RANKL may have a negative regulatory effect on STAT5a activity.

Avicularin Alleviates Osteoporosis in Ovariectomized Mice by Inhibiting Osteoclastogenesis through NF-κB Pathway Inhibition

Osteoporosis (OP) is mainly manifested by bone loss and bone degeneration. OP is considered a risk factor for pathological fractures, as well as impacts the health of middle-aged and elderly individuals. Drug therapy remains the main treatment scheme for OP; however, its efficacy is limited and has been associated with serious side effects. Therefore, it is important to develop new, effective, and safe treatment methods for OP. Avicularin (AL) is a flavonoid and quercetin derivative from various plants. Our study showed that AL disrupts osteoclast activation and resorptive function via inhibition of the RANKL-induced osteoclast differentiation together with the resorption capacity of bone marrow-derived macrophages (BMMs). Hence, AL prevents the activation and resorptive activity of osteoclasts. The results of qPCR showed that genes related to osteoclasts exhibited downregulated expression after AL treatment. Furthermore, AL inhibited RANKL-induced phosphorylation as well as degradation of the inhibitor IκBα of the NF-κB pathway, together with P65 phosphorylation in BMMs. We used an OP mouse model that was established by ovariectomy (OVX). Relative to untreated OP mice, mice that received AL treatment showed a significant increase in bone mineral density; however, the expression of TRAP, NFATC1, mmp9, and CTX-1 was significantly reduced. These results indicate that AL disrupts osteoclastogenesis via inhibition of the NF-κB pathway, which in turn improves OVX-induced OP.

[Treatment options for external inflammatory root resorption]

THE AIM OF THE STUDY

Was to compare the efficacy of various treatment options for external inflammatory root resorption according to literature data.

MATERIALS AND METHODS

Literature was searched in electronic databases «eLibrary» and «PubMed» for key words «external inflammatory resorption treatment», «external inflammatory resorption management». Inclusion criteria comprised publications in Russian or English, clinical and experimental studies, full description of treatment protocol and obtained results. Studies with no full text, describing root resorption of orthodontic origin, clinical cases and clinical case series were excluded from the study.

RESULTS

The problem of external inflammatory root resorption is poorly described in the Russian scientific literature. There are no registered protocols for its prevention and treatment or therapeutic agents with proved efficacy available in Russia. The only accessible approach for external inflammatory root resorption remains timely pulp extirpation after dental trauma which importance is underlined by all authors involved in the field of dental trauma studies. MTA and calcium hydroxide being popular as intracanal medications still have significant inconveniences as they potentially provoke root dentine fractures or replacement resorption.

CONCLUSION

There is a need for elaboration and implementation of new prevention and treatment options for external inflammatory root resorption after dental trauma.

Cathepsin K degrades osteoprotegerin to promote osteoclastogenesis in vitro

Osteoblasts produce the receptor activator of nuclear factor-kappa B ligand (RANKL) and osteoprotegerin, the inducer and the suppressor of osteoclast differentiation and activation. We previously proposed that the degradation of osteoprotegerin by lysine-specific gingipain of Porphyromonas gingivalis and neutrophil elastase is one of the mechanisms of bone resorption associated with infection and inflammation. In the present study, we found that cathepsin K (CTSK) also degraded osteoprotegerin in an acidic milieu and the buffer with a pH of 7.4. The 37 k fragment of osteoprotegerin produced by the reaction with CTSK was further degraded into low molecular weight fragments, including a 13 k fragment, depending on the reaction time. The N-terminal amino acid sequence of the 37 k fragment matched that of the intact osteoprotegerin, indicating that CTSK preferentially hydrolyzes the death domain-like region of osteoprotegerin, not its RANKL-binding region. The 13 k fragment of osteoprotegerin was the C-terminal 13 k portion within the RANKL-binding region of the 37 k fragment. Finally, CTSK restored RANKL-dependent osteoclast differentiation that was suppressed by the addition of osteoprotegerin. Collectively, CTSK is a possible positive regulator of osteoclastogenesis.

Pulsed electromagnetic fields as a promising therapy for glucocorticoid-induced osteoporosis

Glucocorticoid-induced osteoporosis (GIOP) is considered the third type of osteoporosis and is accompanied by high morbidity and mortality. Long-term usage of glucocorticoids (GCs) causes worsened bone quality and low bone mass via their effects on bone cells. Currently, there are various clinical pharmacological treatments to regulate bone mass and skeletal health. Pulsed electromagnetic fields (PEMFs) are applied to treat patients suffering from delayed fracture healing and non-unions. PEMFs may be considered a potential and side-effect-free therapy for GIOP. PEMFs inhibit osteoclastogenesis, stimulate osteoblastogenesis, and affect the activity of bone marrow mesenchymal stem cells (BMSCs), osteocytes and blood vessels, ultimately leading to the retention of bone mass and strength. However, the underlying signaling pathways via which PEMFs influence GIOP remain unclear. This review attempts to summarize the underlying cellular mechanisms of GIOP. Furthermore, recent advances showing that PEMFs affect bone cells are discussed. Finally, we discuss the possibility of using PEMFs as therapy for GIOP.

Effect of Bifidobacterium on osteoclasts: TNF-α/NF-κB inflammatory signal pathway-mediated mechanism

Osteoporosis is a systemic multifactorial bone disease characterized by low bone quality and density and bone microstructure damage, increasing bone fragility and fracture vulnerability. Increased osteoclast differentiation and activity are important factors contributing to bone loss, which is a common pathological manifestation of bone diseases such as osteoporosis. TNF-a/NF-κB is an inflammatory signaling pathway with a key regulatory role in regulating osteoclast formation, and the classical pathway RANKL/RANK/OPG assists osteoclast formation. Activation of this inflammatory pathway promotes the formation of osteoclasts and accelerates the process of osteoporosis. Recent studies and emerging evidence have consistently demonstrated the potential of probiotics to modulate bone health. Secretions of Bifidobacterium, a genus of probiotic bacteria in the phylum Actinobacteria, such as short-chain fatty acids, equol, and exopolysaccharides, have indicated beneficial effects on bone health. This review discusses the molecular mechanisms of the TNF-a/NF-κB inflammatory pathway in regulating osteoclast formation and describes the secretions produced by Bifidobacterium and their potential effects on bone health through this pathway, opening up new directions for future research.

The Role of procollagen type 1 amino-terminal propertied (P1NP) Cytochrome P450 (CYPs) and Osteoprotegerin (OPG) as Potential Bone function markers in Prostate Cancer Bone Metastasis

Background: Procollagen type I amino-terminal propeptide (PINP) is often present during osteoblast development and could be a biomarker of early bone development. Osteoprotegerin (OPG) may protect tumor cells from apoptosis. Cytochrome P450 enzymes help tumor development and treatment (CYPs). Cytochrome P450 activates and deactivates anticancer drugs and procarcinogens.

Objective: The study examined the amounts of a diagnostic marker of bone formation, the amino terminal propeptide of type I procollagen (PINP), Osteoprotegerin (OPG), and P450, in prostate cancer patients at different stages and its ability to detect osteoblastic metastases.

Methods: ELISA was used to measure PINP, OPG, and P450 levels in 30 prostate cancer patients. (n = 32) and healthy men’s serum (n = 36).

Results: Prostate cancer patients had higher blood levels of PINP, OPG, and P450 than healthy persons (301.3±134.9, 980±467.2, and 84.2±28.4 pg/mL, respectively). Compared to I+II prostate cancer patients, III+IV patients showed higher serum PINP, OPG, and P450 levels (P 0.001). OPG, P450, and PINP had statistically significant Area under the ROC curve (0.9467, P= 0.0001, 0.91, P= 0.0001, and 0.6977, P= 0.4035) in prostate cancer patients.

Conclusions: Metastatic prostate cancer patients had greater PINP, OPG, and P450 levels, according to our findings. PINP, OPG, and P450 levels may affect prostate cancer progression. These findings imply that serum PINP, OPG, and P450 levels may predict and diagnose prostate cancer.

IL-6 Plays a Critical Role in Stromal Fibroblast RANKL Induction and Consequent Osteoclastogenesis in Ameloblastoma Progression

Ameloblastoma (AB) is the most common benign, epithelial odontogenic tumor that occurs in the jawbone. AB is a slow-growing, benign epithelial tumor but shows locally invasive growth, with bone resorption or recurrence if not adequately resected. From these points of view, understanding the mechanism of AB-induced bone resorption is necessary for better clinical therapy and improving patients' quality of life. In bone resorption, osteoclasts play critical roles, and RANKL is a pivotal regulator of osteoclastogenesis. However, the source of RANKL-expressing cells in the AB tumor microenvironment is controversial, and the mechanism of osteoclastogenesis in AB progression is not fully understood. In this study, we investigated the distribution of the RNA expression of RANKL in AB specimens. We found that PDGFRα- and S100A4-positive stromal fibroblasts expressed RANKL in the AB tumor microenvironment. Moreover, we analyzed the mechanisms of osteoclastogenesis in the AB tumor microenvironment using the human AB cell line AM-1 and a human primary periodontal ligament fibroblast cells. The results of histopathologic and in vitro studies clarified that the interaction between AB cells and stromal fibroblasts upregulated IL-6 expression and that AB cells induced RANKL expression in stromal fibroblasts and consequent osteoclastogenesis in AB progression.

Underdiagnosis in Background of Emerging Public Health Challenges Related to Peri-Implant Diseases: An Interventional Split-Mouth Study

Peri-implant diseases are an emerging public health problem, and it's considered that limitations of standard diagnostics play the role herein. The study objective was the estimation of pathological bone resorption at clinical and biological level in patients with peri-implant mucositis (PIM) and peri-implantitis (PI) before and 6 months after standard treatment and to compare them with healthy controls (HC). The split-mouth interventional study included 60 patients affected with PIM or PI. Patients that also presented at least one more HC were enrolled in the study and underwent standard non-surgical and surgical treatment, respectively. Standard clinical parameters and soluble levels of RANKL were measured in peri-implant crevicular fluid baseline and 6 months following treatment. Clinical parameters and RANKL significantly decreased following treatment in PIM and PI. However, bleeding on probing and probing depth remained significantly increased when compared to HC. RANKL answered requests for biomarker of peri-implant diseases, its baseline levels were significantly increased in PIM and PI, they decreased following treatment and reached HC in peri-implantitis, while in PIM RANKL remained significantly increased. Presence of pathological bone resorption in patients lacked its clinical signs, and respective persistence following treatment suggest the need for biomarker-supported diagnosis for timely diagnosis of peri-implantitis and appropriate orientation of respective management strategies.

The effects of seeding density and osteoclastic supplement concentration on osteoclastic differentiation and resorption

The bone resorbing osteoclasts are a complex type of cell essential for in vivo bone remodeling. There is no consensus on medium composition and seeding density for in vitro osteoclastogenesis, despite the importance thereof on osteoclastic differentiation and activity. The aim of this study was to investigate the relative effect of monocyte or peripheral blood mononuclear cell (PBMC) seeding density, osteoclastic supplement concentration and priming on the in vitro generation of functional osteoclasts, and to explore and evaluate the usefulness of commonly used markers for osteoclast cultures. Morphology and osteoclast formation were analyzed with fluorescence imaging for tartrate resistant acid phosphatase (TRAP) and integrin β3 (Iβ3). TRAP release was analyzed from supernatant samples, and resorption was analyzed from culture on Corning® Osteo Assay plates. In this study, we have shown that common non-standardized culturing conditions of monocyte or PBMCs had a significant effect on the in vitro generation of functional osteoclasts. We showed how increased osteoclastic supplement concentrations supported osteoclastic differentiation and resorption but not TRAP release, while priming resulted in increased TRAP release as well. Increased monocyte seeding densities resulted in more and large TRAP positive bi-nuclear cells, but not directly in more multinucleated osteoclasts, resorption or TRAP release. Increasing PBMC seeding densities resulted in more and larger osteoclasts and more resorption, although resorption was disproportionally low compared to the monocyte seeding density experiment. Exploration of commonly used markers for osteoclast cultures demonstrated that Iβ3 staining was an excellent and specific osteoclast marker in addition to TRAP staining, while supernatant TRAP measurements could not accurately predict osteoclastic resorptive activity. With improved understanding of the effect of seeding density and osteoclastic supplement concentration on osteoclasts, experiments yielding higher numbers of functional osteoclasts can ultimately improve our knowledge of osteoclasts, osteoclastogenesis, bone remodeling and bone diseases.

Normalization of the Immunological Microenvironment and Sustained Minimal Residual Disease Negativity: Do We Need Both for Long-Term Control of Multiple Myeloma?

Over the past two decades, the treatment landscape for multiple myeloma (MM) has progressed significantly, with the introduction of several new drug classes that have greatly improved patient outcomes. At present, it is well known how the bone marrow (BM) microenvironment (ME) exerts an immunosuppressive action leading to an exhaustion of the immune system cells and promoting the proliferation and sustenance of tumor plasma cells. Therefore, having drugs that can reconstitute a healthy BM ME can improve results in MM patients. Recent findings clearly demonstrated that achieving minimal residual disease (MRD) negativity and sustaining MRD negativity over time play a pivotal prognostic role. However, despite the achievement of MRD negativity, patients may still relapse. The understanding of immunologic changes in the BM ME during treatment, complemented by a deeper knowledge of plasma cell genomics and biology, will be critical to develop future therapies to sustain MRD negativity over time and possibly achieve an operational cure. In this review, we focus on the components of the BM ME and their role in MM, on the prognostic significance of MRD negativity and, finally, on the relative contribution of tumor plasma cell biology and BM ME to long-term disease control.

Differential Recovery Patterns of the Maxilla and Mandible after Eliminating Nasal Obstruction in Growing Rats

Although nasal obstruction (NO) during growth causes maxillofacial growth suppression, it remains unclear whether eliminating the NO affects maxillary and mandibular growth differentially. We aimed to clarify whether eliminating NO can help regain normal maxillofacial growth and to determine the optimal intervention timing. Forty-two 4-week-old male Wistar rats were randomly divided into six groups. Their left nostril was sutured to simulate NO over different durations in the experimental groups; the sutures were later removed to resume nasal breathing. Maxillofacial morphology was assessed using microcomputed tomography. Immunohistochemical changes in hypoxia-inducible factor (HIF)-1α, osteoprotegerin (OPG), and receptor activator of nuclear factor kappa-B ligand (RANKL) of the condylar cartilage were evaluated to reveal the underlying mechanisms of these changes. Maxillary length was significantly lower in rats with NO for ≥5 weeks. In groups with NO for ≥7 weeks, the posterior mandibular length, ramus height, thickness of the hypertrophic cell layer in the condylar cartilage, HIF-1α levels, and RANKL levels were significantly lower and OPG levels and RANKL/OPG were significantly higher than those in the control group. Our findings suggest that eliminating NO is effective in regaining maxillofacial growth. Moreover, the optimal timing of intervention differed between the maxilla and mandible.

FAEE exerts a protective effect against osteoporosis by regulating the MAPK signalling pathway

CONTEXT

Ferulic acid ethyl ester (FAEE) is abundant in Ligusticum chuanxiong Hort. (Apiaceae) and grains, and possesses diverse biological activities; but the effects of FAEE on osteoporosis has not been reported.

OBJECTIVE

This study investigated whether FAEE can attenuate osteoclastogenesis and relieve ovariectomy-induced osteoporosis via attenuating mitogen-activated protein kinase (MAPK).

MATERIALS AND METHODS

We stimulated RAW 264.7 cells with receptor activator of NF-κB ligand (RANKL) followed by FAEE. The roles of FAEE in osteoclast production and osteogenic resorption of mature osteoclasts were evaluated by tartrate resistant acid phosphatase (TRAP) staining, expression of osteoclast-specific genes, proteins and MAPK. Ovariectomized (OVX) female Sprague-Dawley rats were administered FAEE (20 mg/kg/day) for 12 weeks to explore its potential in vivo, and then histology was undertaken in combination with cytokines analyses.

RESULTS

FAEE suppressed RANKL-induced osteoclast formation (96 ± 0.88 vs. 15 ± 1.68) by suppressing the expression of osteoclast-specific genes, proteins and MAPK signalling pathway related proteins (p-ERK/ERK, p-JNK/JNK and p-P38/P38) in vitro. In addition, OVX rats exposed to FAEE maintained their normal calcium (Ca) (2.72 ± 0.02 vs. 2.63 ± 0.03, p < 0.05) balance, increased oestradiol levels (498.3 ± 9.43 vs. 398.7 ± 22.06, p < 0.05), simultaneously reduced levels of bone mineral density (BMD) (0.159 ± 0.0016 vs. 0.153 ± 0.0025, p < 0.05) and bone mineral content (BMC) (0.8 ± 0.0158 vs. 0.68 ± 0.0291, p < 0.01).

DISCUSSION AND CONCLUSIONS

These findings suggested that FAEE could be used to ameliorate osteoporosis by the MAPK signalling pathway, suggesting that FAEE could be a potential therapeutic candidate for osteoporosis.

Updated trabecular bone score accounting for the soft tissue thickness (TBSTT) demonstrated significantly improved bone microstructure with denosumab in the FREEDOM TBS post hoc analysis

TBS algorithm has been updated to account for regional soft tissue noise. In postmenopausal women with osteoporosis, denosumab improved tissue thickness-adjusted TBS vs placebo independently of bone mineral density over 3 years, with the magnitude of changes from baseline or placebo numerically greater than body mass index-adjusted TBS.

INTRODUCTION

To evaluate the effect of denosumab on bone microarchitecture assessed by trabecular bone score (TBS) in the FREEDOM study using the updated algorithm that accounts for regional soft tissue thickness (TBSTT) in dual-energy X-ray absorptiometry (DXA) images and to compare percent changes from baseline and placebo with classical body mass index (BMI)-adjusted TBS (TBSBMI).

METHODS

Postmenopausal women with lumbar spine or total hip bone mineral density (BMD) T score <  - 2.5 and ≥  - 4.0 received placebo or denosumab 60 mg subcutaneously every 6 months. TBSBMI and TBSTT were assessed on lumbar spine DXA scans at baseline and months 1, 12, 24, and 36 in a subset of 279 women (129 placebo, 150 denosumab) who completed the 3-year FREEDOM DXA substudy and rolled over to open-label extension study.

RESULTS

Baseline characteristics were similar between groups. TBSTT in the denosumab group showed numerically greater changes from both baseline and placebo than TBSBMI at months 12, 24, and 36. Denosumab led to progressive increases in BMD (1.2, 5.6, 8.1, and 10.5%) and TBSTT (0.4, 2.3, 2.6, and 3.3%) from baseline to months 1, 12, 24, and 36, respectively. Both TBS changes were significant vs baseline and placebo from months 12 to 36 (p < 0.0001). As expected, BMD and TBSTT were poorly correlated both at baseline and for changes during treatment.

CONCLUSION

In postmenopausal women with osteoporosis, denosumab significantly improved bone microstructure assessed by TBSTT over 3 years. TBSTT seemed more responsive to denosumab treatment than TBSBMI and was independent of BMD.

BHLHE40 promotes osteoclastogenesis and abnormal bone resorption via c-Fos/NFATc1

Background

Dysregulated osteoclast activity due to altered osteoclast differentiation causes multiple bone diseases. Osteoclasts are multinucleated giant cells derived from hematopoietic stem cells and play a major role in bone absorption. However, the mechanisms underlying the tight regulation of osteoclast differentiation in multiple pathophysiological status remain unknown.

Results

We showed that Bhlhe40 upregulation is tightly associated with osteoclast differentiation and osteoporosis. Functionally, Bhlhe40 promoted osteoclast differentiation in vitro, and Bhlhe40 deficiency led to increased bone mass and decreased osteoclast differentiation in vivo. Moreover, Bhlhe40 deficient mice resisted estrogen deficiency and aging-induced osteoporosis. Mechanism study showed that the increase in bone mass due to Bhlhe40 deficiency was a cell intrinsic defect in osteoclast differentiation in these mice. BHLHE40 upregulated the gene expression of Fos and Nfatc1 by directly binding to their promoter regions. Notably, inhibition of Fos/Nfatc1 abrogated the enhanced osteoclast differentiation induced by BHLHE40 overexpression.

Conclusions

Our research reveals a novel Bhlhe40/c-Fos/Nfatc1 axis involved in regulating osteoclastogenesis and shows that osteoporosis caused by estrogen deficiency and aging can be rescued by regulating Bhlhe40 in mice. This may help in the development of a new strategy for the treatment of osteoporosis.

Aberrant paracrine signalling for bone remodelling underlies the mutant histone-driven giant cell tumour of bone

Oncohistones represent compelling evidence for a causative role of epigenetic perturbations in cancer. Giant cell tumours of bone (GCTs) are characterised by a mutated histone H3.3 as the sole genetic driver present in bone-forming osteoprogenitor cells but absent from abnormally large bone-resorbing osteoclasts which represent the hallmark of these neoplasms. While these striking features imply a pathogenic interaction between mesenchymal and myelomonocytic lineages during GCT development, the underlying mechanisms remain unknown. We show that the changes in the transcriptome and epigenome in the mesenchymal cells caused by the H3.3-G34W mutation contribute to increase osteoclast recruitment in part via reduced expression of the TGFβ-like soluble factor, SCUBE3. Transcriptional changes in SCUBE3 are associated with altered histone marks and H3.3^G34W enrichment at its enhancer regions. In turn, osteoclasts secrete unregulated amounts of SEMA4D which enhances proliferation of mutated osteoprogenitors arresting their maturation. These findings provide a mechanism by which GCTs undergo differentiation in response to denosumab, a drug that depletes the tumour of osteoclasts. In contrast, hTERT alterations, commonly found in malignant GCT, result in the histone-mutated neoplastic cells being independent of osteoclasts for their proliferation, predicting unresponsiveness to denosumab. We provide a mechanism for the initiation of GCT, the basis of which is dysfunctional cross-talk between bone-forming and bone-resorbing cells. The findings highlight the role of tumour/microenvironment bidirectional interactions in tumorigenesis and how this is exploited in the treatment of GCT.

Cathepsin K in Pathological Conditions and New Therapeutic and Diagnostic Perspectives

Cathepsin K (CatK) is a part of the family of cysteine proteases involved in many important processes, including the degradation activity of collagen 1 and elastin in bone resorption. Changes in levels of CatK are associated with various pathological conditions, primarily related to bone and cartilage degradation, such as pycnodysostosis (associated with CatK deficiency), osteoporosis, and osteoarthritis (associated with CatK overexpression). Recently, the increased secretion of CatK is being highly correlated to vascular inflammation, hypersensitivity pneumonitis, Wegener granulomatosis, berylliosis, tuberculosis, as well as with tumor progression. Due to the wide spectrum of diseases in which CatK is involved, the design and validation of active site-specific inhibitors has been a subject of keen interest in pharmaceutical companies in recent decades. In this review, we summarized the molecular background of CatK and its involvement in various diseases, as well as its clinical significance for diagnosis and therapy.

Cytokine-mediated immunomodulation of osteoclastogenesis

Cytokines are an important set of proteins regulating bone homeostasis. In inflammation induced bone resorption, cytokines, such as RANKL, TNF-α, M-CSF, are indispensable for the differentiation and activation of resorption-driving osteoclasts, the process we know as osteoclastogenesis. On the other hand, immune system produces a number of regulatory cytokines, including IL-4, IL-10 and IFNs, and limits excessive activation of osteoclastogenesis and bone loss during inflammation. These unique properties make cytokines powerful targets as rheostat to maintain bone homeostasis and for potential immunotherapies of inflammatory bone diseases. In this review, we summarize recent advances in cytokine-mediated regulation of osteoclastogenesis and provide insights of potential translational impact of bench-side research into clinical treatment of bone disease.

The role of secreted osteoclastogenic factor of activated T cells in bone remodeling

The process of bone remodeling is connected with the regulated balance between bone cell populations (including bone-forming osteoblasts, bone-resorbing osteoclasts, and the osteocyte). And the mechanism of bone remodeling activity is related to the major pathway, receptor activator of nuclear factor kappaB (RANK)/RANK ligand (RANKL)/osteoprotegerin (OPG) signaling axis. Recently, researchers have found a novel cytokine secreted by activated T cells, which is related to osteoclastogenesis in the absence of osteoblasts or RANKL, leading to bone destruction. They name it the secreted osteoclastogenic factor of activated T cells (SOFAT). SOFAT has been proven to play an essential role in bone remodeling, like mediating the bone resorption in rheumatoid arthritis (RA) and periodontitis. In this review, we outline the latest research concerning SOFAT and discuss the characteristics, location, and regulation of SOFAT. We also summarize the clinical progress of SOFAT and assume the future therapeutic target in some diseases related to bone remodeling.

The origins and formation of bone-resorbing osteoclasts

Osteoclasts (OCLs) are hematopoietic cells whose physiological function is to degrade bone. OCLs are key players in the processes that determine and maintain the mass, shape, and physical properties of bone. OCLs adhere to bone tightly and degrade its matrix by secreting protons and proteases onto the underlying surface. The combination of low pH and proteases degrades the mineral and protein components of the matrix and forms a resorption pit; the degraded material is internalized by the cell and then secreted into the circulation. Insufficient or excessive activity of OCLs can lead to significant changes in bone and either cause or exacerbate symptoms of diseases, as in osteoporosis, osteopetrosis, and cancer-induced bone lysis. OCLs are derived from monocyte-macrophage precursor cells whose origins are in two distinct embryonic cell lineages - erythromyeloid progenitor cells of the yolk sac, and hematopoietic stem cells. OCLs are formed in a multi-stage process that is induced by the cytokines M-CSF and RANKL, during which the cells differentiate, fuse to form multi-nucleated cells, and then differentiate further to become mature, bone-resorbing OCLs. Recent studies indicate that OCLs can undergo fission in vivo to generate smaller cells, called "osteomorphs", that can be "re-cycled" by fusing with other cells to form new OCLs. In this review we describe OCLs and discuss their cellular origins and the cellular and molecular events that drive osteoclastogenesis.

Effect of Lymphocyte Subsets on Bone Density in Senile Osteoporosis: A Retrospective Study

Background

Several studies have shown that lymphocyte subsets can mediate the occurrence of osteoporosis (OP); however, the predictive ability of lymphocyte subsets in senile OP has not been elucidated.

Purpose

To investigate the ability of lymphocyte subsets to predict senile osteoporosis (OP).

Methods and Materials

This study included 44 patients with senile OP and 44 without OP. Dual-energy X-ray absorptiometry (DEXA) was used to determine bone mineral density (BMD). Flow cytometry was used to analyze the absolute counts of the lymphocyte subsets and cytokine levels. Finally, the correlation between BMD and lymphocyte subset counts in the two groups was analyzed.

Results

There were no significant differences in age, sex, or weight between the OP and non-OP groups. The absolute counts of total T lymphocytes and CD8+ T lymphocytes in the OP group were significantly lower than those in the non-OP group. The levels of IFN-γ or TNF-α in the OP group were significantly higher or lower, respectively, than those in the non-OP group. PCA showed that age, BMI, total T lymphocytes, CD4+ T lymphocytes, CD8+ T lymphocytes, and B lymphocytes were the principal components of senile OP. The linear regression equation showed that BMD of the right femoral neck significantly decreased with a decline in CD8+ T lymphocyte counts.

Conclusion

BMD decreased with a decrease in CD8+ T lymphocytes. The mechanism by which lower lymphocyte subsets lead to lower BMD may be related to abnormal bone metabolism caused by immune aging. Therefore, we considered that CD8+ T lymphocytes could be used to predict the incidence of senile OP.

Thiaplakortone B attenuates RANKL-induced NF-κB and MAPK signaling and dampens OVX-induced bone loss in mice

Osteoclasts play an important role in maintaining the relative stability of bone mass. Abnormal number and function of osteoclasts are closely related to osteoporosis and osteolytic diseases. Thiaplakortone B (TPB), a natural compound derived from the Great Barrier Reef sponge Plakortis lita, has been reported to inhibit the growth of the malaria parasite, Plasmodium falciparum, but its effect on osteoclastogenesis has not been previously investigated. In our study, we found that TPB suppresses the receptor activator of nuclear factor-κB (NF-κB) ligand (RANKL)-induced osteoclast formation and resorption activity by tartrate-resistant acid phosphatase (TRAcP) staining, immunofluorescence staining of F-actin belts and hydroxyapatite resorption assay. Furthermore, using quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting analysis, we discovered that TPB inhibits osteoclast-specific genes and proteins expression. Mechanistically, TPB blocks multiple upstream pathways including calcium oscillation, NF-κB, mitogen-activated protein kinase (MAPK) and nuclear factor of activated T cells 1(NFATc1) signaling pathways. In vivo, TPB could dampen bone loss in an ovariectomy (OVX) mouse model by micro-CT assessment and histological staining. Therefore, TPB may serve as a potential therapeutic candidate for the treatment of osteoporosis and osteolysis.

Postmenopausal Osteoporosis: A Literature Review

A substantial proportion of the population of females in India falls in the perimenopausal and postmenopausal age groups. One of the complications associated with older age in women is the weakening of bones and the fall in bone mineral density (BMD). This has a severe debilitating consequence in a woman’s life and leads to reduced quality of life along with a greater incidence of fractures. If the fracture involves the hip or the vertebrae, it can cause immobility and be devastating. Postmenopausal osteoporosis is linked with the deficiency of estrogen that occurs with the cessation of the function of the ovaries as age progresses. The function of estrogen in the bone remodeling process is very well understood after years of research; estrogen plays a part in both the formation of bone as well as the prevention of the resorption of bone. A diagnosis can be made by dual-energy X-ray absorptiometry (DEXA). It is the gold standard and can spot low bone density at particular sites. The treatment options are selected according to the severity and rate of progression and factors pertaining to each patient. All postmenopausal women should be made aware of this disorder, and they should be encouraged to cultivate a healthy lifestyle through the implementation of a proper diet and inculcation of a regular exercise routine. Smoking and drinking alcohol should be limited, and calcium and vitamin D supplementation should be started in all women of the postmenopausal age group with or without osteoporosis. In patients who have been diagnosed with the disorder, pharmacological intervention is done. Drugs should be selected based on their side effects and contradictions. Follow-up is essential, and patient compliance should be carefully monitored. This article attempts to review the existing literature on this very prevalent disorder to spread awareness about it so that all postmenopausal women can take the necessary steps to prevent the weakening of their bones, and deal with its progression.

Mitochondrial fatty acid β-oxidation is important for normal osteoclast formation in growing female mice

Skeletal remodeling is an energy demanding process that is linked to nutrient availability and the levels of metabolic hormones. While recent studies have examined the metabolic requirements of bone formation by osteoblasts, much less is known about the energetic requirements of bone resorption by osteoclasts. The abundance of mitochondria in mature osteoclasts suggests that the production of an acidified micro-environment conducive to the ionization of hydroxyapatite, secretion of matrix-degrading enzymes, and motility during resorption requires significant energetic capacity. To investigate the contribution of mitochondrial long chain fatty acid β-oxidation to osteoclast development, we disrupted the expression of carnitine palmitoyltransferase-2 (Cpt2) in myeloid-lineage cells. Fatty acid oxidation increases dramatically in bone marrow cultures stimulated with RANKL and M-CSF and microCT analysis revealed that the genetic inhibition of long chain fatty acid oxidation in osteoclasts significantly increases trabecular bone volume in female mice secondary to reduced osteoclast numbers. In line with these data, osteoclast precursors isolated from Cpt2 mutants exhibit reduced capacity to form large-multinucleated osteoclasts, which was not rescued by exogenous glucose or pyruvate, and signs of an energetic stress response. Together, our data demonstrate that mitochondrial long chain fatty acid oxidation by the osteoclast is required for normal bone resorption as its inhibition produces an intrinsic defect in osteoclast formation.

Identification of a binding site on soluble RANKL that can be targeted to inhibit soluble RANK-RANKL interactions and treat osteoporosis

One of the major challenges for discovering protein-protein interaction inhibitors is identifying selective and druggable binding sites at the protein surface. Here, we report an approach to identify a small molecular binding site to selectively inhibit the interaction of soluble RANKL and RANK for designing anti-osteoporosis drugs without undesirable immunosuppressive effects. Through molecular dynamic simulations, we discovered a binding site that allows a small molecule to selectively interrupt soluble RANKL-RANK interaction and without interfering with the membrane RANKL-RANK interaction. We describe a highly potent inhibitor, S3-15, and demonstrate its specificity to inhibit the soluble RANKL-RANK interaction with in vitro and in vivo studies. S3-15 exhibits anti-osteoporotic effects without causing immunosuppression. Through in silico and in vitro experiments we further confirm the binding model of S3-15 and soluble RANKL. This work might inspire structure-based drug discovery for targeting protein-protein interactions.

Biochemical characterization of a disease-causing human osteoprotegerin variant

Recently, a human mutation of OPG was identified to be associated with familial forms of osteoarthritis. This missense mutation (c.1205A =  > T; p.Stop402Leu) occurs on the stop codon of OPG, which results in a 19-residue appendage to the C-terminus (OPG+19). The biochemical consequence of this unusual sequence alteration remains unknown. Here we expressed OPG+19 in 293 cells and the mutant OPG was purified to homogeneity by heparin affinity chromatography and size exclusion chromatography. We found that in sharp contrast to wildtype OPG, which mainly exists in dimeric form, OPG+19 had a strong tendency to form higher-order oligomers. To our surprise, the hyper-oligomerization of OPG+19 had no impact on how it binds cell surface heparan sulfate, how it inhibits RANKL-induced osteoclastogenesis and TRAIL-induced chondrocytes apoptosis. Our data suggest that in biological contexts where OPG is known to play a role, OPG+19 functions equivalently as wildtype OPG. The disease-causing mechanism of OPG+19 likely involves an unknown function of OPG in cartilage homeostasis and mineralization. By demonstrating the biochemical nature of this disease-causing OPG mutant, our study will likely help elucidating the biological roles of OPG in cartilage biology.

Factors secreted by monosodium urate crystal-stimulated macrophages promote a proinflammatory state in osteoblasts: a potential indirect mechanism of bone erosion in gout

BACKGROUND

Tophi are lesions commonly present at sites of bone erosion in gout-affected joints. The tophus comprises a core of monosodium urate (MSU) crystals surrounded by soft tissue that contains macrophages and other immune cells. Previous studies found that MSU crystals directly reduce osteoblast viability and function. The aim of the current study was to determine the indirect, macrophage-mediated effects of MSU crystals on osteoblasts.

METHODS

Conditioned medium from the RAW264.7 mouse macrophage cell line cultured with MSU crystals was added to the MC3T3-E1 mouse osteoblastic cell line. Conditioned medium from the THP-1 human monocytic cell line cultured with MSU crystals was added to primary human osteoblasts (HOBs). Matrix mineralization was assessed by von Kossa staining. Gene expression was determined by real-time PCR, and concentrations of secreted factors were determined by enzyme-linked immunosorbent assay.

RESULTS

In MC3T3-E1 cells cultured for 13 days in an osteogenic medium, the expression of the osteoblast marker genes Col1a1, Runx2, Sp7, Bglap, Ibsp, and Dmp1 was inhibited by a conditioned medium from MSU crystal-stimulated RAW264.7 macrophages. Mineral staining of MC3T3-E1 cultures on day 21 confirmed the inhibition of osteoblast differentiation. In HOB cultures, the effect of 20 h incubation with a conditioned medium from MSU crystal-stimulated THP-1 monocytes on osteoblast gene expression was less consistent. Expression of the genes encoding cyclooxygenase-2 and IL-6 and secretion of the proinflammatory mediators PGE2 and IL-6 were induced in MC3T3-E1 and HOBs incubated with conditioned medium from MSU crystal-stimulated macrophages/monocytes. However, inhibition of cyclooxygenase-2 activity and PGE2 secretion from HOBs indicated that this pathway does not play a major role in mediating the indirect effects of MSU crystals in HOBs.

CONCLUSIONS

Factors secreted from macrophages stimulated by MSU crystals attenuate osteoblast differentiation and induce the expression and secretion of proinflammatory mediators from osteoblasts. We suggest that bone erosion in joints affected by gout results from a combination of direct and indirect effects of MSU crystals.

Chi3L1 is a therapeutic target in bone metabolism and a potential clinical marker in patients with osteoporosis

BMP2 is clinically used as an ectopic bone inducer and plays a significant role in bone development, formation, and diseases. Chitinase 3-like 1 protein (Chi3L1) is found in the skeletal system. However, Chi3L1-mediated bone metabolism and aging-related bone erosion via BMP2 signaling have not yet been demonstrated. Herein, Chi3L1 increased BMP2-induced osteoblast differentiation in mesenchymal precursor cells and human primary osteoblasts. Chi3L1^KO(-/-) showed abnormal bone development, and primary osteoblasts isolated from Chi3L1^KO(-/-) exhibited impaired osteoblast differentiation and maturation. Chi3L1 also potentiated BMP2 signaling and RUNX2 expression in primary osteoblasts. Chi3L1 interacted with BMPRIa, which increased the surface expression of BMPRIa and promoted BMP2 signaling to induce osteoblast differentiation. Chi3L1^KO(-/-) mice showed bone formation reduced with a decrease in RUNX2 expression in calvarial defects. Chi3L1^KO(-/-) mice exhibited aging-related osteoporotic bone loss with decreases in the levels of RUNX2 and OPG, while serum PYD level and osteoclast number increased. Chi3L1 increased OPG via non-canonical BMP2 signaling in osteoblasts, which suppressed osteoclastogenesis in BMMs. Furthermore, ROC analysis showed that serum Chi3L1 level clinically decreased in osteoporosis patients. Our findings demonstrate that Chi3L1 promotes bone formation, suppresses osteoclastogenesis, and prevents aging-related osteoporosis.

Water Extract of Piper longum Linn Ameliorates Ovariectomy-Induced Bone Loss by Inhibiting Osteoclast Differentiation

Piper longum linn has traditionally been used for the treatment of respiratory and gastrointestinal disorders in India. Although various pharmacological effects of P. longum have been studied, its effects on bone have not been clearly elucidated. Therefore, this study examined the inhibitory effect of the water extract of P. longum Linn (WEPL) on osteoclast differentiation. WEPL directly affected the osteoclast precursors and suppressed osteoclast differentiation in vitro. In addition, the expression levels of c-Fos and nuclear factor of activated T cells 1, a critical transcription factor for osteoclastogenesis, were significantly downregulated by WEPL via the suppression of the receptor activator of nuclear factor (NF)-κB ligand-induced mitogen-activated protein kinase and NF-κB signaling pathways. Consistent with the in vitro results, oral administration of WEPL (100 and 300 mpk) to ovariectomized mice for six weeks relieved the OVX-induced bone loss. We also identified phytochemicals in WEPL that are reported to exert inhibitory effects on osteoclastogenesis and/or bone loss. Collectively, the findings of our study indicate that WEPL has an anti-osteoporotic effect on OVX-induced bone loss by diminishing osteoclast differentiation, suggesting that it may be useful to treat several bone diseases caused by excessive bone resorption.

Neuronal Guidance Molecules in Bone Remodeling and Orthodontic Tooth Movement

During orthodontic tooth movement, mechanically induced remodeling occurs in the alveolar bone due to the action of orthodontic forces. The number of factors identified to be involved in mechanically induced bone remodeling is growing steadily. With the uncovering of the functions of neuronal guidance molecules (NGMs) for skeletal development as well as for bone homeostasis, NGMs are now also among the potentially significant factors for the regulation of bone remodeling during orthodontic tooth movement. This narrative review attempts to summarize the functions of NGMs in bone homeostasis and provides insight into the currently sparse literature on the functions of these molecules during orthodontic tooth movement. Presently, four families of NGMs are known: Netrins, Slits, Semaphorins, ephrins and Eph receptors. A search of electronic databases revealed roles in bone homeostasis for representatives from all four NGM families. Functions during orthodontic tooth movement, however, were only identified for Semaphorins, ephrins and Eph receptors. For these, crucial prerequisites for participation in the regulation of orthodontically induced bone remodeling, such as expression in cells of the periodontal ligament and in the alveolar bone, as well as mechanical inducibility, were shown, which suggests that the importance of NGMs in orthodontic tooth movement may be underappreciated to date and further research might be warranted.

Osteoclast biology in the single-cell era

Osteoclasts, the only cells that can resorb bone, play a central role in bone homeostasis as well as bone damage under pathological conditions such as osteoporosis, arthritis, periodontitis, and bone metastasis. Recent studies using single-cell technologies have uncovered the regulatory mechanisms underlying osteoclastogenesis at unprecedented resolution and shed light on the possibility that there is heterogeneity in the origin, function, and fate of osteoclast-lineage cells. Here, we discuss the current advances and emerging concepts in osteoclast biology.

Where is bone science taking us?

Bone science has over the last decades unraveled many important pathways in bone and mineral metabolism and the interplay between genetic factors and the environment. Some of these discoveries have led to the development of pharmacological treatments of osteoporosis and rare bone diseases. Other scientific avenues have uncovered a role for the gut microbiome in regulating bone mass, which have led to investigations on the possible therapeutic role of probiotics in the prevention of osteoporosis. Huge advances have been made in identifying the genes that cause rare bone diseases, which in some cases have led to therapeutic interventions. Advances have also been made in understanding the genetic basis of the more common polygenic bone diseases, including osteoporosis and Paget's disease of bone (PDB). Polygenic profiles are used for establishing genetic risk scores aiming at early diagnosis and intervention, but also in Mendelian randomization (MR) studies to investigate both desired and undesired effects of targets for drug design.

Comparison of two non-union models with damaged periosteum in mice: Segmental defect and pin-clip fixation versus transverse fracture and K-wire stabilization

Despite growing knowledge about the mechanisms of fracture healing, non-union formation still represents a major complication in trauma and orthopedic surgery. Non-union models in mice gain increasing interest, because they allow investigating the molecular and cellular mechanisms of failed fracture healing. These models often use segmental defects to achieve non-union formation. Alternatively, failed fracture healing can be induced by transverse fractures with additional periosteal injury. The present study systematically compared the reliability of these two approaches to serve as non-union model. A 0.6 mm K-wire was inserted into the femora of CD-1 mice in a retrograde fashion and a closed transverse femoral fracture was created. Subsequently, the fracture site was exposed and the periosteum was cauterized. This approach was compared with a well-established non-union model involving the pin-clip fixation of a 1.8 mm segmental defect. The callus tissue was analyzed by means of radiography, biomechanics, histology and Western blotting. At 10 weeks after surgery 10 out of 12 femora (83.3 %) of the K-wire group showed a non-union formation. The pin-clip model resulted in 100 % non-union formation. The K-wire group showed increased bone formation, osteoclast activity and bending stiffness when compared to the group with pin-clip fixation. This was associated with a higher expression of bone formation markers. However, the number of CD31-positive microvessels was reduced in the K-wire group, indicating an impaired angiogenic capacity after periosteal cauterization. These findings suggest that the pin-clip model is more reliable for the study of non-union formation in mice. The K-wire model including periosteal injury by cauterization however, may be particularly applied in preclinical studies which explore the effects of damaged periosteum and reduced angiogenic capacity to trauma-induced fractures.

Molecular Biomarkers in Peri-Implant Health and Disease: A Cross-Sectional Pilot Study

Background: The aim of this feasibility study was to investigate the concentration level of CCL-20/MIP-3α, BAFF/BLyS, IL-23, RANKL, and Osteoprotegerin in the Peri-Implant Crevicular Fluid (PICF), from patients diagnosed with peri-implant mucositis and peri-implantitis, and to compare them with PICF from patients with healthy implants. Methods: Participants with at least one dental implant with healthy peri-implant tissues, peri-implant mucositis, or peri-implantitis were included. PICF was collected using paper strips from healthy and diseased peri-implant sites (n = 19). Biomarker levels were analyzed using a custom Multiplex ELISA Assay Kit. Results: In comparison to peri-implant health, the peri-implant mucositis group showed an increased concentration of CCL-20 MIP-3α, BAFF/BLyS, IL-23, RANKL, and Osteoprotegerin. The peri-implantitis group had the lowest median concentration of Osteoprotegerin (1963 ng/mL); this group had a similar concentration of RANKL (640.84 ng/mL) when compared to the peri-implant health group. BAFF/BLyS (17.06 ng/mL) showed the highest concentration in the peri-implantitis group. Conclusions: This feasibility study suggests that IL-23 and RANKL may help to elucidate the pathogenesis during the conversion from peri-implant health to peri-implantitis. Further research is required in BAFF/BLyS for the early diagnosis of peri-implantitis.

Specnuezhenide suppresses diabetes-induced bone loss by inhibiting RANKL-induced osteoclastogenesis

Diabetes osteoporosis is a chronic complication of diabetes mellitus (DM) and is associated with osteoclast formation and enhanced bone resorption. Specnuezhenide (SPN) is an active compound with anti-inflammatory and immunomodulatory properties. However, the roles of SPN in diabetic osteoporosis remain unknown. In this study, primary bone marrow macrophages (BMMs) were pretreated with SPN and were stimulated with receptor activator of nuclear factor kappa B ligand (RANKL; 50 ng/mL) to induce osteoclastogenesis. The number of osteoclasts was detected by tartrate-resistant acid phosphatase (TRAP) staining. The protein levels of cellular oncogene fos/nuclear factor of activated T cells c1 (c-Fos/NFATc1), nuclear factor kappa-B (NF-κB), and mitogen-activated protein kinases (MAPKs) were evaluated by western blot analysis. NF-κB luciferase assays were used to examine the role of SPN in NF-κB activation. The DM model group received a high-glucose, high-fat diet and was then intraperitoneally injected with streptozotocin (STZ). Micro-CT scanning, serum biochemical analysis, histological analysis were used to assess bone loss. We found that SPN suppressed RANKL-induced osteoclast formation and that SPN inhibited the expression of osteoclast-related genes and c-Fos/ NFATc1. SPN inhibited RANKL-induced activation of NF-κB and MAPKs. In vivo experiments revealed that SPN suppressed diabetes-induced bone loss and the number of osteoclasts. Furthermore, SPN decreased the levels of bone turnover markers and increased the levels of runt-related transcription factor 2 (RUNX2), osteoprotegerin (OPG), calcium (Ca) and phosphorus (P). SPN also regulated diabetes-related markers. This study suggests that SPN suppresses diabetes-induced bone loss by inhibiting RANKL-induced osteoclastogenesis, and provides an experimental basis for the treatment of diabetic osteoporosis.

Phospholipase D2 controls bone homeostasis by modulating M-CSF-dependent osteoclastic cell migration and microtubule stability

Phospholipase D2 (PLD2), a signaling protein, plays a central role in cellular communication and various biological processes. Here, we show that PLD2 contributes to bone homeostasis by regulating bone resorption through osteoclastic cell migration and microtubule-dependent cytoskeletal organization. Pld2-deficient mice exhibited a low bone mass attributed to increased osteoclast function without altered osteoblast activity. While Pld2 deficiency did not affect osteoclast differentiation, its absence promoted the migration of osteoclast lineage cells through a mechanism involving M-CSF-induced activation of the PI3K–Akt–GSK3β signaling pathway. The absence of Pld2 also boosted osteoclast spreading and actin ring formation, resulting in elevated bone resorption. Furthermore, Pld2 deletion increased microtubule acetylation and stability, which were later restored by treatment with a specific inhibitor of Akt, an essential molecule for microtubule stabilization and osteoclast bone resorption activity. Interestingly, PLD2 interacted with the M-CSF receptor (c-Fms) and PI3K, and the association between PLD2 and c-Fms was reduced in response to M-CSF. Altogether, our findings indicate that PLD2 regulates bone homeostasis by modulating osteoclastic cell migration and microtubule stability via the M-CSF-dependent PI3K–Akt–GSK3β axis.

A signaling protein that regulates bone resorption may prove a useful target in treating skeletal conditions such as osteoporosis and rheumatoid arthritis. Bone is synthesized by cells called osteoblasts, while osteoclasts trigger bone resorption, keeping the skeleton healthy. Imbalances in this recycling process are common in bone disorders. Je-Young Choi and Hyun-Ju Kim at Kyungpook National University in Daegu, South Korea, and co-workers demonstrated that phospholipase D2 (PLD2), a membrane protein, directly regulates bone resorption in mice. Mice without the Pld2 gene had increased osteoclast activity, resulting in low bone mass. The absence of PLD2 promotes the migration of osteoclasts via a particular signaling pathway. This increased the organization of microtubules, polymers that help form the cytoskeleton. The results suggest that regulating PLD2 activity could form the basis of a future treatment method.

The role of C5a-C5aR1 axis in bone pathophysiology: A mini-review

Bone remodeling is a physiological, dynamic process that mainly depends on the functions of 2 cell types: osteoblasts and osteoclasts. Emerging evidence suggests that complement system is crucially involved in the regulation of functions of these cells, especially during inflammatory states. In this context, complement component 5a (C5a), a powerful pro-inflammatory anaphylatoxin that binds the receptor C5aR1, is known to regulate osteoclast formation and osteoblast inflammatory responses, and has thus been proposed as potential therapeutic target for the treatment of inflammatory bone diseases. In this review, we will analyze the role of C5a-C5aR1 axis in bone physiology and pathophysiology, describing its involvement in the pathogenesis of some of the most frequent inflammatory bone diseases such as rheumatoid arthritis, and also in osteoporosis and bone cancer and metastasis. Moreover, we will examine C5aR1-based pharmacological approaches that are available and have been tested so far for the treatment of these conditions. Given the growing interest of the scientific community on osteoimmunology, and the scarcity of data regarding the role of C5a-C5aR1 axis in bone pathophysiology, we will highlight the importance of this axis in mediating the interactions between skeletal and immune systems and its potential use as a therapeutic target.

Inflammatory stimuli alter bone marrow composition and compromise bone health in the malnourished host

Inflammation has a role in the pathogenesis of childhood malnutrition. We investigated the effect of malnutrition and inflammatory challenge on bone marrow composition and bone health. We studied an established murine model of moderate acute malnutrition at baseline and after acute inflammatory challenge with bacterial lipopolysaccharide (LPS), a surrogate of Gram-negative bacterial sepsis, or Leishmania donovani, the cause of visceral leishmaniasis. Both of these infections cause significant morbidity and mortality in malnourished children. Of the 2 stimuli, LPS caused more pronounced bone marrow changes that were amplified in malnourished mice. LPS challenge led to increased inflammatory cytokine expression (Il1b, Il6, and Tnf), inflammasome activation, and inflammatory monocyte accumulation in the bone marrow of malnourished mice. Depletion of inflammatory monocytes in Csfr1-LysMcre-DT malnourished mice significantly reduced the inflammasome activation and IL1-ß production after LPS challenge. The inflammatory challenge also led to increased expansion of mesenchymal stem cells (MSCs), bone marrow adiposity, and expression of genes (Pparg, Adipoq, and Srbp1) associated with adipogenesis in malnourished mice. This suggests that inflammatory challenge promotes differentiation of BM MSCs toward the adipocyte lineage rather than toward bone-forming osteoblasts in the malnourished host. Concurrent with this reduced osteoblastic potential there was an increase in bone-resorbing osteoclasts, enhanced osteoclast activity, upregulation of inflammatory genes, and IL-1B involved in osteoclast differentiation and activation. The resulting weakened bone formation and increased bone resorption would contribute to the bone fragility associated with malnutrition. Lastly, we evaluated the effect of replacing lipid rich in omega-6 fatty acids (corn oil) with lipid-rich in omega-3 fatty acids (fish oil) in the nutrient-deficient diet. LPS-challenged malnourished mice that received dietary fish oil showed decreased expression of inflammatory cytokines and Rankl and reduced osteoclast differentiation and activation in the bone marrow. This work demonstrates that the negative effect of inflammatory challenge on bone marrow is amplified in the malnourished host. Increasing dietary intake of omega-3 fatty acids may be a means to reduce inflammation and improve bone health in malnourished children.

TGF-beta pathway inhibition as the therapeutic acceleration of diabetic bone regeneration

Bone regeneration and fracture healing are impaired in diabetic patients due to defective functions of associated cells. Thus, the search for molecular causes and new treatment strategies are of particular clinical relevance. We investigated the gene expression profile of bones from type 2 diabetic (db^- /db^- ) mice and wild-type (wt) mice by comparative microarray analyses before and after placing tibial defects and examined the expression of several osteogenesis- and osteoclastogenesis-related markers by quantitative real-time polymerase chain reaction. In regenerating wt bones, pathways related to, for example, inhibition of matrix metalloproteases were activated, whereas in db^- /db^- bones activation of pathways related to, for example, osteoarthritis, transforming growth factor-beta (Tgfb), or hypoxia-inducible factor 1a were detected during regeneration. We defined the Tgfb pathway as a potential therapeutic target and locally applied a single dose (0.5 µg) of the Tgfb 1, 2, and 3 neutralizing antibody 1D11 on tibial defects in db^- /db^- mice (n = 7). Seven days postoperation, histological and immunohistochemical stainings were performed. Decreased bone regeneration, osteogenic differentiation, osteoclast invasion, and angiogenesis in db^- /db^- mice were significantly restored by local 1D11 application in comparison to the phosphate-buffered saline controls. Thus, local treatment of db^- /db^- bony defects with Tgfb neutralizing antibody 1D11 might be considered a good candidate for the successful acceleration of bone regeneration.

Clinical and Biochemical Effects of Smoking on Non-Surgical Periodontal Treatment in Grade III Stage C Periodontitis Patients

Objective: The purpose of this study was to evaluate the effect of smoking on clinical parameters and the serum and saliva levels of RANKL, OPG, and IL-34 in periodontitis stage III grade C (III-C) patients after non-surgical periodontal treatment (NSPT). Methods: A total of 60 subjects, 40 periodontitis-III-C patients (20 smokers and 20 non-smokers) and 20 non-smoker periodontally healthy individuals, were included. All clinical periodontal parameters were recorded, and unstimulated saliva and serum samples were collected from all patients at baseline, but at 1 and 3 months only from periodontitis patients (N=40). Saliva and serum levels of RANKL, OPG, and IL-34 were analyzed by ELISA. Results: At baseline only whole mouth probing depth (PD) and percent of sites with PD>5mm were higher in smokers than non-smoker periodontitis patients (p

The Gestational Effects of Maternal Bone Marker Molecules on Fetal Growth, Metabolism and Long-Term Metabolic Health: A Systematic Review

Fetal exposure in adverse environmental factors during intrauterine life can lead to various biological adjustments, affecting not only in utero development of the conceptus, but also its later metabolic and endocrine wellbeing. During human gestation, maternal bone turnover increases, as reflected by molecules involved in bone metabolism, such as vitamin D, osteocalcin, sclerostin, sRANKL, and osteoprotegerin; however, recent studies support their emerging role in endocrine functions and glucose homeostasis regulation. Herein, we sought to systematically review current knowledge on the effects of aforementioned maternal bone biomarkers during pregnancy on fetal intrauterine growth and metabolism, neonatal anthropometric measures at birth, as well as on future endocrine and metabolic wellbeing of the offspring. A growing body of literature converges on the view that maternal bone turnover is likely implicated in fetal growth, and at least to some extent, in neonatal and childhood body composition and metabolic wellbeing. Maternal sclerostin and sRANKL are positively linked with fetal abdominal circumference and subcutaneous fat deposition, contributing to greater birthweights. Vitamin D deficiency correlates with lower birthweights, while research is still needed on intrauterine fetal metabolism, as well as on vitamin D dosing supplementation during pregnancy, to diminish the risks of low birthweight or SGA neonates in high-risk populations.

Bone Disease in Multiple Myeloma: Biologic and Clinical Implications

Multiple Myeloma (MM) is a hematologic malignancy characterized by the proliferation of monoclonal plasma cells localized within the bone marrow. Bone disease with associated osteolytic lesions is a hallmark of MM and develops in the majority of MM patients. Approximately half of patients with bone disease will experience skeletal-related events (SREs), such as spinal cord compression and pathologic fractures, which increase the risk of mortality by 20–40%. At the cellular level, bone disease results from a tumor-cell-driven imbalance between osteoclast bone resorption and osteoblast bone formation, thereby creating a favorable cellular environment for bone resorption. The use of osteoclast inhibitory therapies with bisphosphonates, such as zoledronic acid and the RANKL inhibitor denosumab, have been shown to delay and lower the risk of SREs, as well as the need for surgery or radiation therapy to treat severe bone complications. This review outlines our current understanding of the molecular underpinnings of bone disease, available therapeutic options, and highlights recent advances in the management of MM-related bone disease.

Associations of Bone Mineral Density with RANKL and Osteoprotegerin in Arab Postmenopausal Women: A Cross-Sectional Study

Background and objective: There is limited information as to the association of several key bone markers with bone mineral density (BMD) in understudied ethnic groups. This study investigated the relationship between circulating levels of osteoprotegerin (OPG) and receptor activator of nuclear factor kappa-Β ligand (RANKL) with BMD in Arab postmenopausal women. Materials and methods: In this cross-sectional study, a total of 617 Saudi postmenopausal women from the Osteoporosis Registry of the Chair for Biomarkers of Chronic Diseases were included. Anthropometric data, BMD, and biochemical data were retrieved from the registry. Participants were stratified into three groups based on T-score; n = 169 with osteoporosis, n = 282 with osteopenia, and n = 166 normal. Analysis of bone markers including RANKL, OPG, osteocalcin, and N-terminal telopeptide (NTx) was completed using commercially available bioassays. Results: The results suggested that OPG was significantly and positively correlated with age in the osteoporosis group (r = 0.29, p < 0.05), while it was inversely correlated with BMD femoral neck left (r = −0.56, p < 0.001) and BMD femoral neck right (r = −0.37, p < 0.05) in the same group. Moreover, RANKL showed a significant inverse correlation with NTx in the osteopenia group (r = −0.37, p < 0.05). Furthermore, the RANKL/OPG ratio had a positive and significant correlation with BMI (r = 0.34, p < 0.05), BMD femoral neck left (r = 0.36, p < 0.05) and BMD femoral neck right (r = 0.35, p < 0.05) in the osteopenia group. By contrast, it showed a significant inverse correlation with waist to hip ratio in the osteoporosis group (r = −0.38, p < 0.05). Multiple regression analysis showed that OPG contributes to BMD variations in the osteopenia group (p = 0.03). Conclusions: In conclusion, changes in circulating levels of RANKL and OPG might be a protective mechanism contrary to the increased bone loss in postmenopausal women.

Indigenous Nigeria medicinal herbal remedies: A potential source for therapeutic against rheumatoid arthritis

Rheumatoid arthritis (RA) is a debilitating disease associated with locomotion impairment, and conventional therapeutic drugs are not optimal for managing RA. There is an avalanche of medications used for the management of RA. Still, studies have shown that they are associated with severe side effects, including hepatotoxicity, retinopathy, and cardiotoxicity disorders of the central nervous system (CNS), skin, blood, and infections. Complementary and alternative medicine (CAM) is currently gaining attention as a novel panacea for managing debilitating diseases, such as RA. Nigerian folk herbal remedies are replete with a plethora of curative medicine, albeit unvalidated scientifically but with seemingly miraculous provenance. Studies of the identification of bioactive compounds present in these botanicals using advanced spectral analytical techniques have enhanced our understanding of the role of Nigerian herbal remedies in the treatment and management of RA. Interestingly, experimental studies abound that the bioactive compounds present in the extracts of plant botanicals protected animals from the development of RA in different experimental models and reduced the toxicity associated with conventional therapeutics. Validated mechanisms of RA amelioration in human and animal models include suppression of the expression of NF-κB, IL-1β, TNF-α, IL-6, IL-8, IL-17, IL-23, chemokines, TGF-β, RANKL, RANK, iNOS, arginase, COX-2, VEGFA, VEGFR, NFATC1, and TRAP in the synoviocytes. Decreased ROS, NO, MDA, carbonyl groups, and PGE₂ in the synovial fluid increased the expression of PPARα/γ; antioxidant and anti-inflammatory molecules also improve RA etiology. In this mini-review, we discuss the global burden of RA, the novel role of plant-based botanicals as potential therapeutics against signaling pathways in RA. Also addressed is the possible repurposing/reprofiling of plant botanicals to increase their therapeutic index among RA patients that patronize traditional healers in Nigeria with a global projection.

Changes in adiposity over the life course and gene expression in postmenopausal women

BACKGROUND

Early life adiposity and changes in adiposity over the life course are associated with mammographic breast density among postmenopausal women. However, the underlying mechanisms are unknown; therefore, we comprehensively examined the associations of early life body mass index (BMI) and changes in BMI from ages 10, 18 to age at mammogram with growth factor, RANK pathway, and sex hormone gene expression in 372 postmenopausal women.

METHODS

We estimated early life BMI at age 10 using the validated 9-level Stunkard pictogram. We calculated BMI at other ages (18, 30, and current age at mammogram) by dividing weight in kilograms at these ages with height in meters squared. Sequencing for gene expression was performed using the NanoString nCounter system. After adjusting for confounders, we estimated associations using multivariable linear regressions.

RESULTS

A 10 kg/m2 increase in early life BMI at age 10 was associated with a 17.2% decrease in RANKL gene expression (95% confidence interval [CI] = -30.8, -0.9) but was not associated with changes in other markers. BMI changes from ages 10, 18 to age at mammogram were associated with an increase in BMP2 and decreases in RANK, RANKL, and TNFRSF13B gene expression but were not associated with gene expression of other markers. A 10 kg/m2 increase in early life BMI from age 10 to current age was associated with a 7.8% increase in BMP2 (95% CI = -1.4, 17.8), an 8.5% decrease in RANK (95% CI = -13.9, -2.8), a 10.4% decrease in RANKL (95% CI = -16.9, -3.3), and an 8.5% decrease in TNFRSF13B gene expression (95% CI = -13.8, -2.8).

CONCLUSION

The results provide new insights into the biological mechanisms underlying the associations of adiposity changes from early life to adulthood and early life adiposity with mammographic breast density in postmenopausal women.

Targeting signaling pathways in prostate cancer: mechanisms and clinical trials

Prostate cancer (PCa) affects millions of men globally. Due to advances in understanding genomic landscapes and biological functions, the treatment of PCa continues to improve. Recently, various new classes of agents, which include next-generation androgen receptor (AR) signaling inhibitors (abiraterone, enzalutamide, apalutamide, and darolutamide), bone-targeting agents (radium-223 chloride, zoledronic acid), and poly(ADP-ribose) polymerase (PARP) inhibitors (olaparib, rucaparib, and talazoparib) have been developed to treat PCa. Agents targeting other signaling pathways, including cyclin-dependent kinase (CDK)4/6, Ak strain transforming (AKT), wingless-type protein (WNT), and epigenetic marks, have successively entered clinical trials. Furthermore, prostate-specific membrane antigen (PSMA) targeting agents such as ¹⁷⁷Lu-PSMA-617 are promising theranostics that could improve both diagnostic accuracy and therapeutic efficacy. Advanced clinical studies with immune checkpoint inhibitors (ICIs) have shown limited benefits in PCa, whereas subgroups of PCa with mismatch repair (MMR) or CDK12 inactivation may benefit from ICIs treatment. In this review, we summarized the targeted agents of PCa in clinical trials and their underlying mechanisms, and further discussed their limitations and future directions.

Effect of a single-dose denosumab on semen quality in infertile men (the FITMI study): study protocol for a randomized controlled trial

Background

Infertility is a common problem globally and impaired semen quality is responsible for up to 40% of all cases. Almost all infertile couples are treated with either insemination or assisted reproductive techniques (ARTs) independent of the etiology of infertility because no medical treatment exists. Denosumab is an antibody that blocks RANKL signaling and inhibition of testicular RANKL signaling has been suggested to improve semen quality in a pilot study. This RCT aims to assess whether treatment with denosumab can improve spermatogenesis in infertile men selected by serum AMH as a positive predictive biomarker. This paper describes the design of the study.

Methods/design

FITMI is a sponsor-investigator-initiated, double-blinded, placebo-controlled 1:1, single-center, randomized clinical trial. Subjects will be randomized to receive either a single-dose denosumab 60 mg subcutaneous injection or placebo. The study will be carried out at the Department of Growth and Reproduction, Copenhagen University Hospital, Rigshospitalet, Copenhagen. The primary outcome of the study is defined as the difference in sperm concentration (millions pr. mL) one spermatogenesis (80 days) after inclusion.

Discussion

We describe a protocol for a planned RCT aimed at evaluating whether treatment with denosumab can improve the semen quality in infertile men selected by using serum AMH as a positive predictive biomarker. The results will provide evidence crucial for future treatment in a patient group where there is a huge unmet need.

Trial registration

Clinical Trials.gov NCT05212337. Registered on 14 January 2022.

EudraCT 2021–003,451-42. Registered on 23 June 2021.

Ethical committee H-21040145. Registered on 23 December 2021.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13063-022-06478-4.